allow passing in rule explicitly

Author: Martin Zihlmann

src/apispec_webframeworks/flask.py

@@ -120,21 +120,34 @@ def _rule_for_view(
         rule = app.url_map._rules_by_endpoint[endpoint][0]
         return rule
 
+    @staticmethod
+    def _view_for_rule(
+        rule: Rule,
+        app: Optional[Flask] = None,
+    ) -> Union[Callable[..., Any], "RouteCallable"]:
+        if app is None:
+            app = current_app
+        return app.view_functions[rule.endpoint]
+
     def path_helper(
         self,
         path: Optional[str] = None,
         operations: Optional[dict] = None,
         parameters: Optional[List[dict]] = None,
         *,
         view: Optional[Union[Callable[..., Any], "RouteCallable"]] = None,
+        rule: Optional[Rule] = None,
         app: Optional[Flask] = None,
         **kwargs: Any,
     ) -> Optional[str]:
         """Path helper that allows passing a Flask view function."""
-        assert view is not None
+        assert view is not None or rule is not None
         assert operations is not None
 
-        rule = self._rule_for_view(view, app=app)
+        if rule is None:
+            rule = self._rule_for_view(view, app=app)
+        if view is None:
+            view = self._view_for_rule(rule, app=app)
         view_doc = view.__doc__ or ""
         doc_operations = yaml_utils.load_operations_from_docstring(view_doc)
         operations.update(doc_operations)